The prior art contains a number of blood vessel catheters including coronary infusion catheters which are inserted through coronary angiography catheters to position the distal ends of the infusion catheters at selected points in coronary arteries. Coronary infusion catheters include the following types: (1) a polytetrafluoroethylene tube of uniform construction; (2) a PVC tube shrunk onto a metal coil spring body with a distal 20 cm section of the tube extending past the end of the spring body and having a shrunken diameter to form a more flexible distal section to aid in negotiating curves; and (3) a polymer tube having a body section with a reinforcing braid included in the tube wall wherein a distal 20 cm section of the tube extending from the body section does not contain the reinforcing braid. These infusion catheters are usually inserted through a previously installed angiography catheter with the distal end being advanced, under fluoroscopic guidance, from the end of the angiography catheter to the desired site. Difficulty has sometimes been experienced in positioning of prior art catheters in some blood vessels, for example in the left circumflex coronary artery. Vascular trauma has also been experienced by various types of prior art catheters.
Uniform tube type coronary infusion cathethers, such as the polytetrafluoroethylene tube of 2.5 French size, are generally too stiff for the distal end to negotiate tortuous blood vessels without traumatizing the vessels and are generally too flexible to possess desired torque and column characteristics. The torque characteristic concerns the ability to transmit rotational movement from one end of the catheter to the other; catheters must sometimes be rotated in order to direct a curved distal end of the catheter into a selected branch vessel or to follow a vessel curve. The column characteristic concerns the ability to resist buckling of the catheter while being pushed; buckling at the entrance of a guiding catheter or within a vessel produces kinks or sharp bends which make insertion more difficult, or prevents insertion of the distal end of the catheter to the desired site in the blood vessel. Guide wires, i.e. tightly coiled fine metal springs, with or without precurved ends are commonly inserted inside catheters to render the catheters less flexible and to direct the distal end of the catheter in the desired direction. Such guide wires generally can not substantially improve torque characteristics of the catheter, and because of uniformity in flexibility or stiffness throughout their length, can not provide the degree of variation in flexibility or stiffness required to negotiate turns and simultaneously resist buckling.
The prior art catheter type with the PVC tube shrunk on the metal coil spring does provide a variation in stiffness or flexibility between the body section secured on the spring and the distal portion extending from the body portion. However, such coronary infusion catheters of a favorable size, i.e. 2.5 French in the body sections and 2.0 French in the distal section, have relatively small internal diameters through the coil springs and the distal sections preventing insertion of a guide wire and also restricting the flow of medicine. Additionally, the tube wall is relatively thick in the distal section because of shrinkage of a larger tube size limiting the degree of flexibility, and this type of catheter includes a rigid radiopaque tip which tends to traumatize blood vessels.
The reinforced braid type coronary infusion catheter is generally too large, i.e. 4 French in size, and too stiff in its distal section to be readily inserted without excessive risk of vessel traumatization.